The fast method
⚡
1 + 2 + 3 = 6, which is divisible by 3.
How it works
Add the digits; the integer is divisible by 3 when its digit sum is. Every power of 10 has remainder 1 when divided by 3.
Why it works
Every power of 10 has remainder 1 when divided by 3.
Use it when
Applies to integers written in base ten; use absolute value for negative integers.
Watch out for
The rule checks divisibility; it does not calculate the quotient.
Verified examples
Example 1
Is 123 divisible by 3?
1 + 2 + 3 = 6, which is divisible by 3.
YesExample 2
Is 452 divisible by 3?
4 + 5 + 2 = 11, which is not divisible by 3.
NoExample 3
Is 780 divisible by 3?
7 + 8 + 0 = 15, which is divisible by 3.
Yes